Platelet production is now known to be controlled by way of a humoral mechanism much like erythropoiesis, but further research is hampered because of the lack of adequate assay methods. This research project is designed to develop both a bioassay and an immunoassay for thrombopoietin, and to purify and identify the hormone, thrombopoietin. These objectives will be pursued by utilizing a variety of physical, chemical and immunological methods: anti-platelet serum and irradiation will be used to produce thrombopoietin-rich serum; thrombopoietin will be partially purified by several chemical methods; a bioassay procedure for thrombopoietin will be developed; anti-thrombopoietin serum will be raised in rabbits; and further development of an immunoassay for thrombopoietin by use of the hemagglutination-inhibition system will be performed. The development of a reproducible quantitative assay technique for thrombopoietin will make possible studies of thrombopoietin activity in the serum of patients with platelet production disorders. BIBLIOGRAPHIC REFERENCES: McDonald, T.P., R. Clift, C. Nolan, and I.I.E. Tribby. A Comparison of Mice in Rebound-Thrombocytosis with Platelet-Hypertransfused Mice for the Assay of Thrombopoietin. Scand. J. Haematol. 16: 326-334, 1976. McDonald, T.P., M. Cottrell, and R. Clift. Effects of X-Irradiation and Platelet-Specific Antisera on Thrombopoietin Production in Mice. Abstract for the 24th Annual Meeting of the Radiation Research Society, June 27-July 2, 1976, San Francisco, California, p. 83.